How to choose a potato harvester

Bruising is reduced mainly by controlling tuber condition at harvest, cutting drop heights, cushioning every contact surface and running machines slowly. The sources do not agree on drop height, so I give both figures below.

Field and tuber conditions

• Allow 14-21 days of skin set after vine kill (CIP), so the periderm is mature and skinning is limited.
• Harvest when tuber or soil temperature is above 7°C. Cold tubers bruise more easily (USDA, Penn State).
• Keep soil below 25°C. Higher temperatures raise respiration and give soft tubers (Penn State).
• Avoid very wet soil, which sticks, and very dry soil, which increases abrasion (CIP).

Machine and handling practices

• Drop height: USDA advises under 15 cm (6 inches) at every transfer point. Penn State recommends under 30 cm. The tighter limit is the safer target. Drops of more than 6 inches onto a hard surface can cause shatter bruise (USDA).
• Pad all contact surfaces with rubber or foam (Springer), and use rubber-cushioned conveyors and rollers (Penn State).
• Run web and conveyor speeds at the recommended setting. Slower speeds reduce impact damage (Halderson & Henning, 1993, Springer).
• Set blades deep enough, since shallow settings cause cuts (USDA).
• Avoid deep piles or hoppers, which cause pressure bruise on bottom tubers (USDA).
• Transport on clean tarps or in soft-bottom bins (Penn State).

What to look for in a harvester

• Soil separation and clod/stone rejection. Combine harvesters (Grimme, Dewulf, AVR) offer full separation, stone/clod rejection and integrated bulk handling (Penn State and other university extension sources).
• Capacity matched to your acreage. Single-row units are tractor-mounted or trailed. Multi-row machines (2, 4 or 6 rows) handle 5-15 ha/day.
• Adjustable chain speed and blade depth, and factory padding on all surfaces.
• Low-drop transfer points.

Why it matters

• A well-managed mechanical harvest loses 2-5% of tubers, while a poorly adjusted harvester loses 5-15% (USDA, CIP).
• Mechanical damage such as bruising, cuts and skinning affects 5-15% of tubers (Halderson & Henning, 1993).
• Hand harvesting after a digger loses 5-10%, and fully manual harvest loses 10-20% (CIP).
• Blackspot bruising comes from impacts above 150 g force (Halderson & Henning).

Check your results Use bruise panels: strike or roll tubers, then inspect for browning after 24-48 hours. Aim for under 15% bruise incidence, and run regular bruise audits as quality control.

Key takeaway: Time harvest for skin set and warm tubers (above 7°C), keep drops under 15-30 cm, pad every surface and run slowly. Then verify the results with bruise panels.